1. Field of the Invention
Embodiments of the present invention relate to a liquid crystal display (LCD) device, and more particularly, to a method for manufacturing an LCD device. Embodiments of the invention are suitable for a wide scope of applications. In particular, embodiments of the invention are suitable for reducing a non-uniformity associated with a layering topology of the LCD device.
2. Discussion of the Related Art
The progress toward information-driven society has pushed the demand for various display devices. To meet such a demand, efforts have recently been made to develop flat panel display devices such as liquid crystal display (LCD) devices, plasma display panels (PDPs), electro-luminescent display (ELD) devices, vacuum fluorescent display (VFD) devices, and the like. Such flat panel display devices have been applied to various appliances.
In particular, LCDs have been used as a substitute for cathode ray tubes (CRTs) in association in mobile applications because of their superior picture quality, lightness, thinness, and low power consumption. Currently, LCDs are widely used not only as monitors for notebook computers, but also for desktop computers and television (TV) receivers. Successful application of LCDs to more diverse image display devices depends on whether the LCDs can produce high picture quality including high resolution, high brightness, large display area, and the like, while remaining light, thin, and consuming low power.
Generally, an LCD includes a first substrate and a second substrate joined spaced apart from each other, with a liquid crystal material between the first and second substrates. The first substrate includes a plurality of gate lines arranged in one direction and uniformly spaced apart from one another, and a plurality of data lines arranged crossing the gate lines and uniformly spaced apart from one another, to define pixel regions P. The first substrate also includes a plurality of pixel electrodes formed at respective pixel regions P, and a plurality of thin film transistors (TFTs) each formed at a crossing between a corresponding one of the gate lines and a corresponding one of the data lines. A data signal on each data line is applied to a corresponding one of the pixel electrodes in response to a signal applied to a corresponding one of the gate lines.
The second substrate includes a black matrix layer for blocking light incident to a region other than the pixel regions P. The second substrate also includes R, G, and B color filter layers formed at a region corresponding to each pixel region P for displaying color images, and a common electrode formed on the color filter layers to produce a voltage difference with respect to the pixel electrode corresponding to a pixel region.
The liquid crystals of the liquid crystal layer are oriented in a certain direction by an electric field generated between the corresponding pixel electrode and the corresponding common electrode. The amount of light passing through the liquid crystal layer is controlled in accordance with the orientation of the liquid crystal layer, to display a desired image.
The LCD having the above-mentioned driving principle is called a twisted nematic (TN) mode LCD. However, such a TN mode LCD has a narrow view image. In order to overcome the drawback of the TN mode LCD, an in-plane switching (IPS) mode LCD has been developed. In the IPS mode LCD, a pixel electrode and a common electrode are formed on a first substrate at each pixel region of the first substrate such that the pixel electrode and common electrode extend parallel to each other, to generate an in-plane electric field (i.e., horizontal field). The liquid crystal layer is oriented in a certain direction by the in-plane electric field.
Spacers are formed between the first and second substrates to secure a certain space for sealing the liquid crystal layer between the first and second substrates. Spacers are classified into ball spacers and column spacers depending on their shape. The ball spacers have a ball-shape, and are formed on the first and second substrates in accordance with a spraying method. Even after the first and second substrates are joined together, the ball spacers are more or less movable, and have a small area contacting with the first and second substrates. Meanwhile, column spacers are formed on the first and second substrates by an array process. Each column spacer is fixed in the form of a column having a certain height on one of the substrates. Thus, the column spacers have a relatively large area contacting with the first and second substrates, as compared to ball spacers.
FIG. 1 shows a planar view of a first substrate of the related art LCD device. FIG. 2 shows a cross-sectional view along line I-I′ of FIG. 1. Referring to FIGS. 1 and 2, a first substrate 2 includes a black matrix layer 11 formed on the first substrate 2 in a region other than pixel regions P. The first substrate 2 also includes color filter layers 12 12a, 12b and 12c. The color filter layers 12a, 12b and 12c are formed to be spaced apart from one another on the first substrate 2 including the black matrix layers 11. The first substrate 2 also includes a common electrode 13. The common electrode 13 is formed over the entire upper surface of the first substrate 2 including the black matrix layer 11 and the color filter layers 12. The first substrate 2 also includes column spacers 20 respectively formed on the common electrode 13 in regions corresponding to predetermined portions of the black matrix layer 11.
The first substrate 2 faces a second substrate (not shown) having a thin film transistor array (not shown). The first substrate 2 and the second substrate are spaced apart from each other by the column spacers 20.
As shown in FIG. 2, the color filter layers 12, including the color filter layers 12a, 12b and 12c, have different heights to compensate for differences in transmissivity caused by different material characteristics of the R, G and B color filter layers 12a, 12b and 12c. Thus, the color filter layers 12a, 12b and 12c have the same transmissivity. For example, the R, G and B color filter layers 12a, 12b and 12c have different heights h1, h2 and h3, respectively. Accordingly, although the column spacers 20 have the same thickness or height H, the levels of the upper surfaces of the column spacers 20 measured from an upper surface of the first substrate 2 may be different when the column spacers 20 are arranged on different regions. For example, as shown in FIG. 2, when the G, R and B color filter layers 12b, 12a and 12c have a first height h1, a second height h2, and a third height h3, respectively, there is a difference in level among the upper surfaces of column spacers 20 arranged on the respective color filter layers 12a, 12b and 12c, due to the difference in height between the color filter layers 12a, 12b and 12c. In this case, the difference in level between the upper surface of the column spacer 20 formed on the B color filter layer 12c having the largest height (h3) and the upper surface of the column spacer 20 formed on the G color filter layer 12b having the smallest height (h1) corresponds to “h3−h1”. Also, the difference in level between the upper surface of the column spacer formed on the R color filter layer 12a having the largest height (h2) and the upper surface of column spacer formed on the G color filter layer 12b having the smallest height (h1) corresponds to “h2−h1.”
On the other hand, the color filter layers 12a, 12b and 12c may be respectively formed by different patterning processes, so that they have different heights. In this case, the column spacers 20 formed on the respective color filter layers having a difference in height due to the height difference of the color filter layers 12a, 12b and 12c underneath. Thus, it is difficult to ensure a uniform cell gap in different regions between the first substrate 2 and the second substrate, after the first substrate 2 and the second substrate are joined together. The resulting non-uniform cell gap causes a defective image to be displayed.
Thus, the above-mentioned related art LCD device and the above-mentioned related art method for manufacturing the LCD device have the following problems. In the related art LCD device, the column spacers are formed on the color filter layers having a stripe structure, respectively. The respective heights of the column spacers formed on different color filter layers are different. The upper surfaces of the column spacers differ in levels in different regions. Thus, a difference in cell gap occurs in different regions of the LCD device. Such a difference in cell gap causes a variation in optical properties across different regions. As a result, defective image display may occur.
Moreover, the amount of the liquid crystal material filled in the space between the first substrate and the second substrate depends on the column spacer height. However, the difference in level among the upper surfaces of the column spacers caused by the difference in height of the color filter layers makes it difficult to accurately estimate the amount of the liquid crystal material for each liquid crystal cell. Accordingly, the estimated amount of the liquid crystal material could be erroneous, thereby causing an insufficient or excessive filling of the liquid crystal material.
When an insufficient amount of the liquid crystal material is filled between the first and second substrates, the liquid crystal material may shift to a particular portion of the liquid crystal panel and take a long time to be redistributed uniformly across the liquid crystal panel. As a result, the displayed image is defective until the liquid crystal material returns to its original state. On the other hand, when an excessive amount of the liquid crystal material is filled between the first and second substrates, the liquid crystal material flows downward and forms a bulge at the bottom of the liquid crystal panel because of gravity effects to a great expansion of the liquid crystal at high temperature.